The DC matrix converter is a fully regenerative converter that directly converts three-phase AC voltage to a controlled DC output voltage without a DC bus capacitor bank. The problem lies in the control of the converter and the synthesis of the output voltage. Recent efforts have focused on the minimization of commutation losses in the converter's switching elements to increase converter efficiency. The strategy is to synthesize converter output voltage with a minimum number of commutations, based on an analytical tool commonly referred to as "space-vector" analysis. A recent control strategy for the DC matrix converter based upon this approach is disclosed and claimed in commonly-owned, copending U.S. patent application Ser. No. 09/310,393 filed contemporaneously herewith.
In the system of said application, the selected switches are turned on and remain on for two out of three portions of the same or adjacent pulse width modulation periods, in a proper sequence, including two voltage-producing portions and one non-voltage producing portion of each pulse width modulation period.
An aspect of the control strategy that has previously been ignored, however, is the impact on the common-mode output voltage, which is the voltage common to all output phases relative to the neutral point in the system. The magnitude of this voltage directly impacts the sizing of common-mode magnetic components that are commonly used in the design of filters for the suppression of electromagnetic interference (EMI). As a consequence, a control strategy that reduces common-mode voltage will directly reduce sizing requirements for such magnetic components.